How to change the ringtone (sms,email,call) to whatever song I want ?

I know this question is a bit lame but I just dun seem to be able to figure it out. I wanna change my ringtone to some random mp3 but I can't find a way to do that. Can anyone tell me how to do it ? I'm using HTC HD7.

WHAT !! ya gotta be kidding me. I thought I was damn lame for not being able to figure it out. I guess MS is lamer than me in this case. Developers of windows 7 fone use one single ringtone on their phone ? I believe not. ah that's terrible. Even my damn old sony ericsson can do it , no sweat. Damn ! This makes me regret for getting Windows 7 mobile.

Thanks. I know this sounds a bit stupid but I have been using the same ringtone for sms and phone call for almost 5 to 6 years. Now my problem is even if the phone rings I dun seem to realize that it's my phone. LOL. cuz I normally put the phone in my bag, vibration ain't an option here too. Guess, I will just have to train myself to get used to this new sound. Thanks all.-